The body responds to a bleeding skin wound by stopping the invasion of pathogens and arresting the bleeding. Once this has occurred it is necessary to remove foreign bodies and tissue detritus and construct new tissue. The normal wound-healing process can be divided for simplicity into 4 phases:                1. vascular reaction and blood clotting,        2. inflammation,        3. new tissue formation (formation of granulation tissue and reepithelialization), and        4. remodeling.These processes overlap and are partly mutually dependent, so that the sequence only approximately corresponds to the time course of wound healing.        
The vascular reaction phase has the function of preventing major blood losses and entails vasoconstriction, which persists until blood clotting provisionally closes the wound. The processes taking place in the inflammation phase are predominantly catabolic, i.e. breaking down. In this phase of wound healing, granulocytes, macrophages and lymphocytes clean the wound by taking up exogenous material and tissue detritus and breaking it down enzymatically.
The phase of new tissue formation by contrast includes repair, i.e. anabolic responses. An adequate blood supply is a precondition for a wound to heal well, so that new blood vessels are formed (angiogenesis) from as early as the third day after the injury. New connective tissue formation takes place in parallel with the vascularization. Fibroblasts migrate along the fibrin matrix into the wound. They produce the connective tissue ground substance consisting of proteoglycans and collagen fibers, which are crucial for tissue strength.
In healthy tissue, collagen fibers are aligned in particular patterns which follow the main directions of tension. The presence of coenzymes and cofactors such as, for example, ascorbic acid, iron and copper is crucial for collagen synthesis. If there is a deficiency of these substances, wound healing may be impaired. Scar tissue results in this case, being characterized by an unorganized structure of the collagen fibers.
The outgrowth of connective tissue takes place to the same extent as the breakdown of the provisional fibrin matrix (fibrinolysis) and the recanalization again of the closed vessels. The mitotic activity of the fibroblasts terminates with new fiber formation. They are converted on the one hand into fibrocytes, and on the other hand into myofibroblasts. The latter contain contractile elements and are able to contract. In this case, the collagen fibers are tightened and—where possible—aligned according to the main direction of tension of the tissue. As a consequence thereof, the skin tissue which is capable of functioning contracts at the edge of the wound so that only a small defect then remains.
Wound healing requires a balanced equilibrium of contrary actions such as cell proliferation and cell apoptosis, construction and breakdown of blood vessels, and construction and breakdown of collagen. If this equilibrium—especially in the construction and breakdown of collagen fibers—is disturbed in any way it may lead to a hypotrophic, atrophic or hypertrophic scar. The events differentiating normal wound healing from, for example, hypertrophic wound healing start even during development of granulation tissue. The most visible difference in the tissue is the amount and orientation of the collagen fibers. In hypertrophic scar formation, an excess of collagen is produced, and the granulation tissue shows a tendency to construct the collagen fibers in a random and disordered manner.
Hypertrophic scars are raised relative to the surrounding skin and show a large number of variations in size, shape, color and consistency. These characteristics depend firstly on the site and size of the injury and secondly on the chronological development and the personal susceptibility. The ends are normally prominent and end abruptly, sometimes with finger-like projections. The reddish color and the swelling of fresh scars derives from the increased vessel density. Over time, the connective tissue tightens during the remodeling phase, and the blood vessel density declines. The scar therefore sinks somewhat and becomes paler. The remodeling process comprises remodeling of the scar tissue and is the phase of wound healing which lasts longest and may extend for up to 20 years after the injury. This essentially entails restructuring of the collagen fibers, with some of them being broken down by collagenases present in the tissue or else being newly crosslinked.
The general prior art on dressings and wound plasters says nothing about the specific problems arising in the treatment of scars. Thus, EP 0 264 299 B1 discloses a dressing consisting of a water-absorbing sealing pad which in turn is formed by one or more hydrocolloids. The hydrocolloid(s) are dissolved in a binder or mixed therewith.
The pad is firmly and completely gripped by a water-tight cover layer. The pad is, according to the invention, beveled at least around the outer periphery in such a way that the thickness at the edge does not exceed about one quarter of its maximum thickness. Production takes place by a dicasting process under high pressures and at high temperatures. This process is unsuitable for crosslinked polymer gels, for example polyurethane gels.
WO 92/05755 relates to contoured wound contact materials with an adhesive composition layer consisting of swellable hydrocolloids and water-insoluble, viscous constituents, for example, polyisobutylene, rubber, silicone or polyurethane elastomers. In this case, the adhesive composition layer in the edge zone, which layer is of the same type as the adhesive composition in the central zone, has a thickness of less than 0.5 mm (preferably less than 0.3 mm) and a width of at least 5 mm (preferably at least 10 mm). The hydrocolloid-based adhesive composition shows tack even on a moist substrate.
Foam wound contact materials as are obtainable for example from S & N under the name Cutinova® thin and Cutinova® hydro are inter alia described in DE 42 33 289 A1, in DE 196 18 825 A1 and WO 97/43328. The flat polyurethane foam with a thickness of from 1 to 6 mm is covered on one side by a polyurethane film. Plasters of appropriate size are cut out of the baled product. The wound contact material produced in this way surprisingly adheres completely on uptake of wound fluid and moreover does not show the known tendency of hydrocolloids to disintegrate on pronounced swelling, which may lead to residues of the hydrocolloid remaining in the wound.
The large-area wound contact materials which have been cut out are outstandingly suitable for managing chronic or poorly healing wounds of patients requiring hospital care. There is no discussion of a positive or negative effect on scar treatment. In particular, on mechanical stress the product easily peels off because of its cut edges. On contact with moisture, the open cut edges prove to be disadvantageous because water can thereby reach the absorbent layer and leads to swelling and adhesion of the polyurethane foam through penetration of moisture in from the side.
In addition, the significant height of the product (up to 4 mm) and the identical self-adhesive properties at the edge favors the adhesion of dirt and peeling off to adhesion of, for example, items of clothing.
A process for producing a dressing with thin edges consisting of at least two adhesive composition layers is described in EP 0 680 299 A1. The adhesive layers, which may be of the same type or differ in type, correspond to an arrangement of different areas which are connected together and which decrease in size towards the top. Moreover, the individual layers have a stepped profile which, in order to achieve an externally continuous outline, must be covered with a further layer. A further disadvantage is the stepwise slope of the dressing on the side facing the skin, so that contact is irregular thereby at some places in the wound region and wound edge region.
EP 0 919 211 A2 mentions the production of wound dressings with beveled edges from thermoformed plastics backing films which are release coated and have a cavity into which a self-adhesive hydrophilic polymer gel is introduced. The dressings have an adhesive covering layer which is in turn covered with a protective layer. The process is complicated and is unsuitable for wound dressings of “a piece”. In this case too, the dressings are beveled on the side facing the wound.
Finally, mention may also be made of conventional plasters for the care of wounds (for example the fabric plaster Hansaplast® classic from Beiersdorf), which are only conditionally suitable for use as scar plasters. Disadvantages which emerge are the low elasticity and the tendency for the backing material to peel off at the edges of the plaster on mechanical stress when worn for a lengthy period. In addition, the plaster becomes thoroughly wet during daily ablutions or during hand washing and loses adhesiveness. Conventional plasters are visually very conspicuous, impede movements and impair for example the wear comfort in shoes.
Scar dressings differ from known wound care dressings and plasters in being left on the skin over a prolonged period in order to ensure a desired reducing effect. The usual thickness of wound plasters of about 1 mm and more leads with this long duration of wearing to detachment through friction on clothing, bed sheets, skin contacts or during daily washing. For this reason, known dressings or plasters cannot be employed for the indicated purpose. Moreover, the requirements to be met by the scar contact material are quite different from those for wound contact materials.
Scar coverings based on silicone gel, as are described, for example in EP 782457 A1, have the disadvantage that their breathability is lower and they are prone to maceration effects.
The maceration effects are moreover only one disadvantage shown by many known adhesive dressings. The problem with scar-reducing plasters is, on the one hand, skin-kindly and long-lasting adhesion to the skin, and on the other hand painless detachment from the skin without residues. None of the disclosures mentioned provides a proposed solution to this which is acceptable for the manufacturer and for the user.